#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;
using ll = long long;

int main(){
    ll n;
    cin >> n;
    vector<ll> dp(60 , 0);
    dp[0] = 1;
    for(int i = 1; i <= 55; i++){
        dp[i] += dp[i - 1];
        if(i - 2 >= 0)dp[i] += dp[i - 2];
    }
    cout << dp[n] << endl;
    return 0;
}